Field of the Invention
The present invention relates to a high power energy storage device additive and a high power energy storage device comprising the same, and more particularly, to a new lithium ion capacitor additive which is added to a carbon-based material applied as a cathode active material for a lithium ion capacitor such that the new lithium ion capacitor additive is capable of improving capacity and energy density by electrochemically doping a lithium ion onto an anode, and the lithium ion capacitor comprising the lithium ion capacitor additive.
Related Art
With the spread of supply in portable small-sized electric and electronic devices, development of new-model secondary batteries such as a nickel hydrogen battery, a lithium secondary battery, a super capacitor, and a lithium ion capacitor is actively being progressed.
An electrochemical capacitor in an electrochemical energy storage device may be divided into an electric double layer capacitor using electric double layer principle and a hybrid super capacitor using electrochemical oxidation-reduction reaction.
An electric double layer capacitor using a physical adsorption reaction of electric charges in an electric double layer has been limited in the application to various application fields due to a low energy density despite excellent output characteristics and lifetime characteristics.
As a means of solving such a problem of the electric double layer capacitor, a lithium ion capacitor among hybrid super capacitors using a carbon-based material that is capable of inserting and extracting lithium ions as an anode active material has been suggested.
The lithium ion capacitor is a secondary battery system of a new concept which combines high power/long lifetime characteristics of an existing electric double layer capacitor (EDLC) with high energy density of a lithium ion battery.
In an electric double layer super capacitor using an activated carbon electrode in both electrodes, charging and discharging are achieved by a non-faradic reaction in which ions are physically adsorbed onto or desorbed from the surface of the electrode. On the other hand, in a lithium ion capacitor, a non-electrochemical reaction in which the ions are physically adsorbed or desorbed occurs in a cathode, and an electrochemical reaction in which lithium ions are electrochemically inserted into or extracted from a graphite layer structure occurs in an anode. Accordingly, the lithium ion capacitor is capable of obtaining a very larger electric capacity than the electric double layer super capacitor.
In order to stably realize high electric capacity characteristics of the lithium ion capacitor, a process of pre-doping a graphite anode with lithium is required. A high energy density can be obtained by pre-doping lithium onto the graphite anode, thereby maintaining an electric potential of the graphite anode at the same electric potential level as that of lithium metal during charging and discharging of the lithium ion capacitor. The lithium ion capacitor can sharply reduce the electric potential of the anode, can realize a high voltage of 3.8 V or higher that is greatly improved than a cell voltage of a conventional electric double layer capacitor of 2.5 V, and can implement a high energy density by pre-doping lithium ions with a high ionization tendency onto the anode.
A conventional method of pre-doping lithium onto the graphite anode adopts a method that metal lithium laminated by an electric potential difference between the anode and metal lithium is melted into the anode only by laminating metal lithium onto the electrode and injecting the metal lithium laminated onto the electrode into an electrolytic solution, thereby short circuiting the anode and metal lithium. That is, the graphite electrode is electrochemically doped with lithium in a state that the two electrodes are separated from each other after dipping the graphite electrode and a lithium metal electrode in the electrolyte.
However, when the electrochemical doping process is a lithium doping process of laminating metal lithium onto the electrode, it is difficult to control the amount of lithium doped onto the anode, it is hard to obtain safety according to lithium metal generated in the doping process, a very slow doping rate of lithium causes an increase in process costs, and the electrochemical doping process becomes a major impediment to universalization of the lithium ion capacitor accordingly.